1. Field of the Invention
The present invention relates to a photoradical polymerization initiator, a radical generator, a photosensitive compound and a photosensitive resin composition containing any of these materials and a product or accessory portions of the product produced using the photosensitive resin composition.
The invention relates, particularly, to a photoradical polymerization initiator, a radical generator and a photosensitive compound which have high heat resistance, do not remain as an independent component in a cured product and have a radical-generating part which can be synthesized in a mild condition, also relates to a photosensitive resin composition containing any of these materials and also to any product among color filters, electronic parts, layer insulation films, wire coating layers, optical materials, optical circuits, optical circuit parts, antireflecting films, holograms and building materials or to an accessory portion of these products, at least a part of which is formed of a cured product of the photosensitive resin composition.
2. Description of the Related Art
Photosensitive resins which are cured or changed in solubility by irradiation of radial rays such as ultra violet rays are generally classified into two categories including a type (positive type) in which an exposed portion is highly soluble and a type (negative type) in which an unexposed portion is highly soluble. In the case of the negative type, the photosensitive resin remains on a substrate and often becomes a part of a product as a functional layer because the photosensitive resin itself is cured and becomes insoluble by exposure. Although the negative type photosensitive resin has been used for, for example, paints, printing inks, adhesives and printing master plates or the like, it has been recently used in wide applications ranging to products such as solder resists for wire protection in print boards, layer insulation films and resists for forming pixels in color filters.
As one of the negative type photosensitive resins which are frequently used in general, there is resin compositions containing a compound having one or more ethylenic unsaturated bonds, a photoradical initiator generating a radical by irradiation with light and, as required, a high molecular compound providing developing ability and softness to a coating layer, an inorganic filler, pigments or the like. When radial rays are applied to this composition, the compounds having an ethylenic unsaturated bond are bonded to each other by a radical reaction and cured as a macromolecule. In this curing reaction, a three-dimensional network structure is developed by a crosslinking reaction, improving the hardness, strength, adhesiveness, resistance to solvent and heat resistance of the resulting cured product.
The photoradical polymerization initiators are roughly classified into a self cleavage type and a hydrogen-drawing type. In the case of the former type, it absorbs light (electromagnetic wave or radial rays) having a specific wavelength, the bond at a part corresponding to that wavelength is cut, radicals are generated in each part cut at this time and a radical reaction starts from these parts. In the case of the latter type, when it absorbs an electromagnetic wave having a specific wave length and put into an excited state, it draws hydrogen from surrounding hydrogen donors. At this time, radicals are generated from each of the drawing one and the drawn one.
Generally, the self-cleavage type has good sensitivity and high radical-generating efficiency, but is unstable to heat, giving rise to the problems concerning the heat resistance, stability and preserving stability of a photosensitive resin composition containing this self-cleavage type. In the case of the hydrogen-drawing type, on the other hand, the hydrogen donor must exist in the vicinity of the excited initiator and the radical-generating efficiency is decided by the magnitude of an energy barrier when drawing hydrogen. Therefore, this type has relatively low sensitivity, but a resin composition containing this type exhibits high stability and preserving stability because no radical is generated unless it is put in an excited state and draws hydrogen.
In the solder resist used for surface coating in a print board, an organic pigment and a filler are compounded to provide thermal resistance and flame resistance. Also, in a resist used for forming pixels of a color filter, a pigment for color indication is compounded. Because these pigments are components absorbing light, a self-cleavage type photoradical initiator is principally used to raise the sensitivity of a photosensitive resin and also the photoradical initiator is compounded in a large amount allowing for a portion which will not fully used in a radical reaction. Here, the portion which is not fully used in a radical reaction includes an unreacted initiator which has not been cleft even by irradiation with light and an initiator whose activity is lost by prohibiting its access to material to be caused reaction because of a reaction in a solid phase even if it is radicalized by cleavage.
A large amount of residues originated from an initiator exists in the cured product after exposure. Among these residues, a photoradical generator which has not been cleft still keeps reactivity even after exposure and therefore denatures a product. Also, a photoradical initiator which has not been cleft and a decomposed material which has been cleft but not consumed in a radical reaction and deactivated is not bonded to a crosslinking structure of a matrix and exists as an independent component in a product, which impairs the quality of a layer. For this, if a decomposed material originated from an initiator is left as it is, there is the problem that it causes deteriorated light resistance, coloring and fading, peeling of a coating layer and the occurrence of cracks or the like, which is a cause of a reduction in the reliability of a final product such as a layer insulation film and solder resist in electronic parts and a resist used for forming pixels in a color filter.
The self-cleavage type photoradical initiator has a strong sublimation tendency and is decomposed by heat. It can be therefore removed from a product by post-baking after exposure and developing at a temperature higher than hundred and several tense degree. However, a large amount of a sublimated material originated from an initiator adheres to the inside of a heater and falls on a product obtained by curing during post-baking, causing product defects, posing a serious problem. Also, a decomposed material of an initiator is involved in the atmosphere around a heater, posing a problem from the viewpoint of operational safety.
It is possible to remove many more residues originated from a radical initiator by changing a post-baking condition to a condition of a higher-temperature and longer-operation time. However, it is difficult to remove the residues completely because of volatilization from a solid. If the condition is made more strict to remove many more impurities originated from a radical initiator, this condition rather causes product defects.
In the meantime, the same curing system using radial rays is applied to a resist for processing electronic parts to be used as a peelable layer and a dry film resist. The processing resist is finally peeled off and is not therefore left in a product. However, the processing step such as formation of copper wirings or the like involves with such a problem that a residue originated from an initiator is eluted in a chemical solution such as ferric chloride and cupric chloride used for the processing from the resist film, so that the life of the chemical solution is shortened.
Moreover, when a photosensitive resin is used as a paint for a protective layer protecting the surface of wall paper and a wall used for buildings, there is a demand for decreasing solvent components and odorous components emitting from whole building material with the view of dealing with sick house syndrome. There is the problem that the use of a highly volatile initiator causes the occurrence of odors even after curing.
From these problems, it has been desired to develop a radical generator and a resin composition which are not volatilized during post-baking and after photo-curing and are substantially freed of components which are originated from a radical generator and remain independently in a coating layer.
As measures to solve these problems, ESACURE KIP 150 (trademark) (manufactured by Nihon Siber Hegner CO., LTD.) and or like introduces a photoradical-generating part into the side chain of a polymer skeleton. This measures ensures that a photoradical generator has plural radical-generating parts in one molecule. Therefore, if any one part in the molecule is radicalized and bonded to a matrix of the coating layer, an unreacted radical-generating part in the same molecule is bonded to the matrix through the polymer skeleton. For this, the photoradical generator is not volatilized during post-baking and does not move in the coating layer, and deterioration of the reliability of a final product is a little.
In this case, however, the photoradical-generating part introduced into the side chain is a self-cleavage type and is easily decomposed by heating to produce a radical, still posing the same problems concerning, for example, the thermal resistance, stability and preserving ability of a photosensitive resin composition containing this product. Although, among the radical-generating parts, the part left on the polymer skeleton after cleavage is bonded to the matrix structure, a part of the decomposed material cleft from the polymer skeleton by a photoradical reaction and post-baking is not consumed by a radical reaction, deactivated and remains independently in the matrix. Therefore, if the decomposed material is left as it is, it adversely affects the qualities of a coating layer, and it is also difficult to remove the decomposed material perfectly by sublimation even if post-baking is carried out.
There is a proposal as to the use of (metha)acrylates having a maleimide group in each publication of International Patent Application Laid-Open WO98/58912 and Japanese patent application Laid-Open No. 2002-3559. These (metha) acrylates as an electron acceptor react with a vinyl ether to generate a radical, because maleimide absorbs electromagnetic waves. Also, these (metha)acrylates draw hydrogen, whereby a radical can also be generated (RADICAL POLYMERIZATION HANDBOOK, NTS Co., Ltd., 1999, page 312). However, maleimide has an ethylenic double bond. If a monomer having both a maleimide group and a (metha)acryl group is radical-polymerized, a crosslinking reaction proceeds and the resulting polymer is gelled. For this, according to each publication of International Patent Application Laid-Open WO98/58912 and Japanese patent application Laid-Open No. 2002-3559, a substituent such as a cyclohexyl group is introduced into a maleimide group to lower the reactivity of the maleimide group by steric hindrance, whereby the above problem is overcome. However, since the reactivity of the maleimide is lowered on the contrary, there is the problem that the efficiency of initiation of a radical reaction is dropped. Also, because the reaction for forming a maleimide group by reacting an acid anhydride with an amine is carried out by a dehydration reaction, a temperature as high as 100° C. or more is required to react highly efficiently without using a catalyst. If it is intended to introduce an ethylenic unsaturated bond directly when forming the maleimide group, there is a synthesis problem that polymerization of the ethylenic unsaturated bond is caused. Also, although a dehydrating catalyst such as acetic acid anhydride may be used to carry out a dehydration reaction. However, this causes a cost increase and also the subsequent refining process is complicated, giving rise to a synthesis problem in any case.
Also, S. Jonsson, et al. propose a photo-reactive crosslinking agent consisting a compound having maleimide groups at both terminals in Proc. Rad Tech 96 (North America Nashville, page 377, 1996). Although this agent reacts rapidly with a vinyl ether, there is the aforementioned synthesis problem because this agent has a maleimide group.
Furthermore, the UV absorption spectrum of a compound having a maleimide part is described in “Industrial Material”, the July issue, 2002, P. 107 to P. 111. According to this spectrum, an unsubstituted maleimide compound has no absorption in wavelengths of 350 nm or more. Therefore, this maleimide compound has no absorption in wavelengths of 365 nm, 405 nm and 436 nm which are major emitting wavelengths of a high pressure mercury lamp as a light source commonly used and therefore, the maleimide group is not expected to be changed at all by these lights.
Because the maleimide group is not sensitive to the above wavelengths, use of maleimide for photocuring is involved with the problem that it is necessary to carry out exposure by using a light source having light emission at a wavelength of 350 nm or less. Although a high pressure mercury lamp also emits light having a wavelength less than 365 nm, these wavelengths fall in the usual range cut by a filter. Even if not cut by a filter, light emission intensity is weak, giving rise to the problem that exposure time is made very longer than that required by a radical generator having absorption in a wavelength of 365 nm in the case of using the same lamp.
In the meantime, Kubo et al. report that when N-methyl-1,8-naphthalimide and an aromatic compound such as p-xylene are irradiated with ultra violet rays in the presence of methanol in an acetonitrile solution, a reaction product of naphthalimide and the aromatic compound is obtained in a high yield (Chemistry Letters, 1999, page 175). There is the description in this report that as its reaction mechanism, naphthalimide which is singlet-excited by ultra violet rays forms an exciplex with the aromatic compound and then the exciplex generates a radical by drawing hydrogen to form a bond between the naphthalimide and the aromatic compound. However, in this document, there is only a description of a reaction in a solution between naphthalimide and low molecular aromatic compounds in a partial scope.
Also, compounds having two naphthalimide parts are disclosed for pharmaceutical use in the publication of WO9402466, for use as electron transfer materials of an electrophotographic photosensitive element in the Japanese patent application Laid-open No. 7-160020 and No. 2001-117247. However, in the former use, these compounds are used as pharmaceuticals. In the latter use, although the invention is directed to a photosensitive material, the naphthalimide compound functions strictly as an electron transfer material, a compound generating a charge by irradiation with light is compounded separately and there is nothing described concerning the function of the naphthalimide compound as a photoradical initiator and concerning a crosslinking reaction.
Also, compounds having a naphthalimide part and an ethylenic unsaturated bond are disclosed in Japanese patent application Laid-open Nos. 62-205108 and 63-218970. However, these compounds are utilized for electrophotographic toners and these documents do not refer to the function of a naphthalimide group as a photoradical generator, the thermal resistance of the naphthalimide and easiness of the synthesis of the naphthalimide.